The present invention relates generally to digital power monitoring. More specifically, the invention relates to a digital power monitoring system which provides the capability to monitor the quality of the power being transmitted through a power system.
Monitoring of electrical power, particularly the measuring and calculating of electrical parameters, provides valuable information for power utilities and their customers. Monitoring of electrical power is important to ensure that the electrical power is effectively and efficiently generated, distributed and utilized. As described in more detail below, knowledge about power parameters such as volts, amps, watts, phase relationship between waveforms, KWH, KVAR, KVARH, KVA, KVAH, power factor, frequency, etc. is of foremost concern for utilities and industrial power users.
Typically, electricity from a utility is fed from a primary substation over a distribution cable to several local substations. At the substations, the supply is transformed by distribution transformers from a relatively high voltage on the distributor cable to the lower voltage at which it is supplied to the end consumer. From the substations, the power is provided to industrial users over a distributed power network which supplies power to various loads. Such loads may be, for example, various power machines.
In such arrangements, utilities need to measure power coming out of or into the generating station or going into a power station. It is important to minimize the phase relationship between the current and voltage waveforms of the power being transmitted to minimize losses. It is also important to minimize the amount of harmonics that are present in the voltage and current waveforms. Also, the ability to detect the presence and magnitude of faults in the power system is important. Thus, accurate measurement of these waveforms is important.
In industrial applications, it is important to continuously monitor the voltage, current, phase, harmonics, faults and 3 phase balance of the power into the machine. These parameters may vary with the machine load. With knowledge of these parameters the industrial user can better adjust, and control the loads to control machines, determine alarm conditions and/or to more efficiently use the power.
Various different arrangements are presently available for monitoring, measuring, and controlling power parameters. Typically, an individual power measuring device which measures specific power system parameters is placed on a given branch or line proximate one of the loads. Such power monitoring devices measure electrical power parameters, such as those described above.
An example of such a system is disclosed in U.S. Pat. No. 5,151,866. In the system disclosed in this patent, a power analyzer system uses discrete analog transducers to convert AC voltage and current signals from a power system to DC output signals. The values from the voltage and the current transducers are then used to calculate the various other desired power parameters.
In addition to monitoring power parameters of a certain load, power monitoring devices have a variety of other applications. For example, power monitoring devices can be used in supervisory control and data acquisition systems (SCADA), process controllers, such as programmable logic controllers (PLC), etc.
Therefore, in view of the above, it is the primary objective of the present invention to provide a power monitoring device which can determine the quality of the power flowing within a power system.
It is a further object of the present invention to provide a power monitoring device with high accuracy.
It is still a further object of the present invention to provide a power monitoring device that contains modular components which can be replaced or interchanged.